Conventionally, a seat belt device mounted on a vehicle is provided with a buckle device which comprises a tongue plate movably attached to the intermediate part of a webbing and a buckle body into and from which the tongue plate is inserted and retracted. This buckle device allows the webbing worn by the occupant to be releasably secured to the vehicle body with ease and reliability.
As described in JP, U, 6-66315, a buckle device is comprised of a metal frame, a hook member which is mounted on or supported by the frame pivotably or swingably and which is engageble with and disengageable from a tongue plate, a lock pin made of metal to lock and unlock the pivotal motion of the hook member, a lock pin holder to hold the lock pin, and a biasing member to urge the lock pin via the lock pin holder, an ejector, a spring member to urge the ejector, a release button which is urged by a coil spring in the same direction as that of withdrawal of the tongue plate to disengage the tongue plate, a base cover and lid cover made of plastics, and so forth.
The foregoing frame includes a base plate part and a pair of side plate parts rising from the base plate part, and the pair of side plate parts are formed with a pair of long holes, and a lock pin is passed through the pair of long holes and mounted across the pair of side plate parts. When inserting the tongue plate, the hook member is made to pivot by the tongue plate via the ejector and comes into engagement with tongue plate, and the lock pin is moved to a first position by the urging force of a biasing member to inhibit the pivoting of the hook member to the disengaging side thereby holding the tongue plate and hook member in an engaged state. The foregoing hook member is pivotally urged in the disengaging direction all the time, and when detaching the tongue plate by releasing the engagement between the tongue plate and the hook member, the hook member is made to pivot to the disengage side by switching the lock pin from a first position to a second position by depressing the release button made of plastics, and thus the tongue plate is made detachable.
The buckle device of JP, U, 6-66311 has a basic configuration comprising a buckle body, a hook member which is pivotally supported by the buckle body and is switchable between engaged and disengaged states with respect to the tongue plate, a lock pin which is supported by the buckle body and is movable between a first position to hold the hook member in engaged state, and a second position to disengage the hook member, a release button which is urged toward the withdrawal direction of the tongue plate by a coil spring, and so forth.
Moreover, in the buckle device of this publication, a lock lever is pivotably mounted near the lock pin to cope with a case in which a pretensioner is equipped to retract the buckle body to the tightening direction to tighten the webbing in an emergency of the vehicle. When inserting the tongue plate, the lock pin is moved to and held in the first position by the lock lever which is pivotally urged by a biasing member, and when detaching the tongue plate, the lock lever is forced to pivot to the non-locked position allowing the lock pin to move to the second position.
Furthermore, near the lock lever is provided a plate-like inertial body which is supported and guided to be movable closing to and away from the lock lever and is constantly urged by a spring member in the direction to move away from the lock lever.
When a buckle body comes into an abrupt stop after it is retracted in the tightening direction of the webbing by a pretensioner which operates in an emergency of the vehicle, the inertial body is moved to lock lever side by an inertial force against the urging force of the spring member and is brought into contact with the lock lever thereby preventing the lock lever from pivoting to the non-lock position. Thus arrangement is made to prevent the detachment of tongue plate from the buckle body, which occurs when the lock pin causes the lock lever to pivot to the non-lock position thereby disengaging the hook member.
The buckle device according to JP, A, 4-58963, comprises a latch member which can come into and out of engagement with a tongue plate, an operation member to release the engagement of the latch member, a lock member which moves to a release position in response to operation of an operational member to disengage the latch member, and a lock mechanism which can prevent disengagement of the latch member. An arrangement is made such that the lock mechanism is provided with a motion restriction member which is pivotably mounted on an operation member and partly protrudes into the movable area of the lock member, and when an impact occurs, the moving lock member comes into abutment with the motion restriction member while part of the motion restriction member, which is pivoting, is in the movable area, and thus the movement of the lock member to the release position is arrested.